1864. ] Vorroxer on Milk, and Dairy Arrangements. 273 
Hydrometers, or lactometers, specially adjusted for testing milk, 
may be obtained at a cheap rate at the philosophical instrument 
makers, and although not capable of furnishing evidence of so exact 
a nature as would be obtained by analysis, these are, nevertheless, very 
much more useful indicators than anyone would be inclined to believe, 
who did not know how far the specific gravity of milk is a test of its 
quality. 
The lactometer was never intended to indicate the relative 
richness of good samples of milk, but to point out whether samples 
of a fair or doubtful appearance had been watered, or were of a 
naturally defective composition; and this purpose it satisfactorily 
fulfils. 
Experiments were instituted in my laboratory for the purpose of 
ascertaining the influence of dilution upon the specific gravity, and 
the quantity of cream thrown up. Water being the standard at 1000 ; 
cream 1012 to 1019, and good milk 1:0820; the temperature being 
always 62° Fahr. 
The following results were obtained :— 
Percentage 
Specific of Cream 
Gravity. in bulk, 
Pure milk at 62° Fahr. . . 6 6 2 1:0320 ; 112i 
PA and 10 per cent. of water at 629 Fahr.  1:0315 5 10 
9 
a 2 .3 a 1°0305 > 9 
” 30 ” ” 1:0290 e 8 
i 40 a4 Z 10190 . 6 
~ 50 5 i-0160° 2 aes 
Experiments made upon milk after being skimmed gave the 
following :— 
Specific 
Gravity. 
Skim milk . : : : 5 : : 5 1:0350 
3; with 10 per cent. water : ° 5 1-0320 
- 20 i. i , 3 1°0265 
7 30 S 5 . . 1°0248 
2 40 Be é ‘ . 10210 
a9 50 ” . : 2 10180 
From these investigations it appears :— 
1. That good new milk has a specific gravity of about 1-030. 
2. That skim milk is a little more dense, being about 1-034. 
3. That milk which hasa specific gravity of 1-025 or less, is 
mixed with water, or naturally very poor. 
4, That when milk is deprived of about 10 per cent. of cream, and 
the original volume is made up by 10 per cent. of water, the specific 
gravity of such skimmed and watered milk is about the same as that 
of good new milk; this circumstance, however, does not constitute any 
serious objection to the hydrometer, as milk skimmed to that extent 
cannot be mixed with water without becoming so blue and transparent, 
that no instrument would be required to detect the adulteration. 
5. That when unskimmed milk is mixed with only 20 per cent. of 
